Electrolytic treatment of articles



United States Patent ELECTROLYTIC TREATMENT 9F ARTHILES .lohn C. Grade,Warren, Ohio, and Arthur Kenneth Graham, fienhintown, Pa., assignors toRockwell- Standard Corporation, (Zoraopolis, Pa, 21 corporation ofPennsylvania No Drawing. Filed Dec. 1, 1%(2, Ser. No. 2,889

6 (Ziaims. (Cl. 294-34) The present invention relates to electrolytictreatment of metallic articles, such as anodic or cathodic treatments inaqueous electrolytes of acids, alkalies, or plating bath compositions.More particularly the present invention relates to a method ofpreventing the development of magnetism in articles of magnetizablemetal so as to obtain electrodeposits of superior smoothness andprotective value by electrically demagnetizing the articles atpredetermined stages in the electrolytic treatments.

During the electrolytic treatment of articles of magnetizable metal intheir preparation for electroplating and in the electrodeposition ofmetals, a major problem in obtaining satisfactory quality is that ofovercoming roughness. From a visual standpoint, this is more serious inbright plating, so prevalent today, than when many electrodeposits wereheavily buffed, as in the early s. From the standpoint of corrosionresistance, roughness is always bad. If the plate is bufied to eliminateroughness, particles are torn out of the coating, thus greatly reducingresistance to corrosion and often creating a pitted appearance.Roughness, like pitting, may also be so fine and widely distributed asto be confused with lack of brightness.

Roughness, when plating articles of magnetizable metal such as steel, iscommonly caused by chips, slivers and other forms of metal debris whichadhere to or are otherwise held to the surface of an article beingelectrolytically treated. Chips and sliver-like metal particles areprobably the most common type particles formed during machining andpolishing operations. For a more detailed explanation and description ofsuch small metallic particles produced during these operations referenceis hereby made to W. L. Pinner, Proc. Amer. Electroplaters Soc. 40,83-89 (1953). Furthermore, such articles may also be magnetized inmachining or polishing, as well asunder the influence of direct currentfields present'in the electrolytic treatments of the plating cycle. Eventhough adhering metal slivers may be removed in these treatments, suchmagnetized articles will attract metal particles present in thesolutions, including the plating bath itself, and roughness will result.(See also R. B. Saltonstall, Electroplating Engineering Handbook,Reinhold Publishing Corp, New York ,pp. 231-232, 1955.)

With certain configurations of articles of magnetizable metallicmaterials to be coated by an electroplating process, as for examplesteel automobile bumpers, an elecrolytic treatment such aselectrocleaning, anodic acid etching and electroplating, create amagnetic field and induce magnetism into the articles. The magnetismthus induced into the articles is of suficient strength to attract smallmagnetizable metallic steel or nickel particles which may be suspendedwithin the treatment baths, so that they adhere to the surface of thearticles. The induced magnetism may also cause attached slivers of metalresulting from polishing the article to stand up on end from the surfaceof the metallic article.

As a consequence, when the articles are carried into the plating bathmetal deposits over these metallic particles result in rough coatings ofinferior quality. Where the slivers stand out from the article surfacethis is even more pronounced.

A further problem resulting from the magnetism of "ice electroplatedarticles made of magnetizable metallic materials arises in measuring theplating thickness. It is the general practice to measure the platingthickness as a production control by means of some conventional form ormagnetic thickness tester, as for example a Magne-Gage. It has beenfound that the residual magnetism in the electroplated article ofmagnetizable metal produces readings in the instrument Which may varyfrom the true value for the thickness being measured to both high andlow values, depending on the degree of induced magnetism in the platedarticles and the relative location of the point of measurement withrespect to the magnetic poles. This is explained in more detail in G. S.Bowman, Monthly Review, Am. Electroplaters Soc. 33, 10445, 1902 (1946);and A. K. Graham and H. L. Pinkerton, Proc. Am. Society for TestingMaterials, vol. 59 (1959).

The present invention has among others, the advantage of overcomingditliculties arising from magnetism induced in articles to beelectroplated. Briefly, this is accomplished by changing the magnitudeand type of current which is normally used in the various electrolytictreatments, over a predetermined period of time at the end of theelectrolytic cycle steps, to a current characterized by periodicreversals of the current flowing combined with a simultaneous diminutionof the magnitude of the current during said period to substantiallyzero.

Accordingly, it is a primary object of the present invention to providea novel process of preventing magnetism from being induced in articlesmade of magnetizable metal as a result of electrolytic treatment priorto electroplating.

It is a further object of this invention to substantially completelyremove any magnetism in an article to be electroplated.

It is yet another object of this invention to improve the quality ofelectroplated articles of steel or any other magnetizable materialproduced by an electroplating process by eliminating roughness ofelectroplated articles caused by magnetic attraction of the articles tosmall metal particles during electrolytic treatments prior to plating.

It is also an object of this invention to provide a novel process forimproving the quality of electroplated articles of steel or magnetizablematerial by eliminating roughness on the surfaces of the articles causedby attached metal particles in general and more especially metallicslivers resulting from polishing by eliminating the tendency for theseslivers to stand up on the surface of said articles under magneticforces.

It is still another object of this invention to provide a novel processto remove the magnetism induced into articles of magnetizable metalduring electroplating thus permitting accurate measurements which maysubsequently be made with a magnetic type of thickness tester as aconvenient, non-destructive, routine production control with acceptableaccuracy.

It is still another object of the present invention to provide a novelelectrolytic process to substantially completely remove any magnetismwhich may have been induced in metallic articles by treatments such asmachining or polishing prior to plating. 1

Further objects and advantages of the present invention will becomeapparent to those skilled in the art from the appended claims andfollowing description.

The method of electrolytic treatment of magnetized articles, accordingto the present invention, will be described particularly as applicablein the production of steel automobile bumpers, but automobile steelhardware and grilles, household appliances, and other plated metallicarticles may be successfully processed in the same manner.

In general, automobile bumpers are made by first .stamping out a formfrom a flat sheet of steel which has ducea smooth finish. After formingthe blank it is transferred to other presses and shaped to a particulardesign of bumper.

The shaped bars are then racked on plating racks to be run through theplating cycle. The'platin'g cycle usually consists of an alkalielectrocleaner, an anodic acid dip followed by another alkalielectrocleaner and acid dip prior to electroplatingwith suitable rinsesin between each treatment step. 'After nickel plating the bars are'usually inspected and bufied and again cleaned and chrostitute soilswhich must be removed first. This is acmium plated. The bufling afternickel plating is usually mild, commonly referred to as a wiping buff,when applied to proprietary bright plated coatings. Buffing is usuallydone to correct for any irregularities in surface appearance as well asroughness.

The apparatus for accomplishing the electrolytic treatments normallygiven to an automobile bumper is similar to that which might be appliedin cycles for other articles made of magnetizable metal. Each of thetreatments involving the use of electric current will inducemagnetisminto the parts being treated. The apparatus in any case will consist ofa tank made of suitable material which holds the waterisolution of thealkali chemicals, acidsor plating compositions, commonly known as theelectrolyte, used in the treatment. The articles ofirnagnetizablematerial arepositioned on a rack or carrier and placed in a particulartreatment bath, so that it Will make electrical contact with a source ofcurrent as either ananode or a cathode as many he required; The other'electrode in each' case will be either a cathode or an anode and will beconnected to the other pole of the current generating equipment. Asource "of direct current, or direct cur rent source which can beperiodically reversed according to some predetermined cycle, isconnected to the electrodes and articles in the treatment tank-throughconventional buses attached to the anode and cathode rods.

The source of current may be a direct current-source, such as a battery,generator or rectifier, combined with suitable relays, reversingswitches, rheostats and timing L mechanisms for controlling themagnitude of the current and for reversing the current at predeterminedtimes and to cause the current to decay from maximum value tosubstantially zero over-selected and predetermined periods in accordancewith the requirements of this inven- Such apparatus is conventional andis disclosed tion. in United States Letters Patent to Grainger, No.2,494,121, issued Jan. 10, 1950; the United States Letters Patent toiernstedt, No. 2,451,341, issued Oct. 12, 1948, or ElectroplatingEngineering Handbook, Reinhold Publishing Corporation, New York; 1955.

It will be appreciated that any suitable apparatus may be devised toproduce the desired electrolytic current cycle and that the cycle may beproduced by simply reversing the flow of current from separate directcurrent sources which may be alternated in accordance with therequirements of the present invention.

In accordance with the present invention, the method for producingfinished nickel-chrome electroplated products having basis metalsof'magnetizable materials first involves manufacturing steps such asmachining and/or forming, followed by polishing, and sometimes buffing,in order to produce the final article in the desired configuration :andwith the specified surface finish. Bumpers are ordinarily not bufiedprior to plating, so that following the conventional operations, thepolished bumper of desired configuration is spray washed in someinstances and is then ready for processing through the plating cycle. Agroup of bumpers are usually mounted on a rack for simultaneousimmersion and treatment in the various treatment steps of the replatingand plating cycle.

It is the usual practice to prepare the surface of the articles forplating by a series of electrolytic cleaning, pickling and polishingtreatments in order to remove organic soil, oxides, and polishing andbuflin-g residues from the sur complished by treating the articles in analkaline electrocleaner, either anodically or cathodically. The cleanermay consist of an aqueous solution'of 8 to 12 oz. gal of a'proprietaryformulation or an equivalent composition compounded from 'a group ofalkali chemicals consisting of hydroxides, carbonates, phosphates andsilicates of sodium 'or potassium. The article is then rinsed to removealkali prior to the next step.

In the case of steel articles, the next step is usually an anodic acidtreatment in a Water solution of sulfuric acid or a mixture of acids.

This treatment serves to remove a certain amount of loose metal from thesurface and to etch the metal in such a Way as to improve the adhesionof the subsequent electrodeposit. A very thorough rinsing must followthis treatment to remove the concentrated acid from the surface of thearticle being processed. n

It is not uncommon to again immerse thearticle in a second alkalineelectrocleaning step similar to the one previously described, thepurpose of which is to insure more complete removal of any residualorganic soil. A

rinse following this treatment is used to remove traces of alkali. v

In the next step the article is usually dipped in a pickling solution,such as 10% by volume hydrochloric acid, to neutralize any alkali and toreactivate the surface after which it is rinsed in water to removetraces of the acid. 7

The current used in the alkaline electrocleaning steps may be a simpledirect current or a cyclic current which i ficiently strong to attractsmall metallic particles of magnetizQable material which are produced byprior manufacturing treatments and which have become dispersed in theelectrolytic treatment bath.

It has been found that merely periodically reversing the flow of thecurrent does not remove magnetism or prevent magnetism from beinginduced into articles of magnetizable material. For instance, anordinary alkali electrocleaning treatment using periodic currentWillmagnetiz'e a rack of automobile bumpers to substantially the sameextent as one using simple direct cleaning and the same total currentflow. This has been found to be true Whether the periodic reversecurrent cycle is made up of equal or unequal portions of positive andnegative current. As a consequence, magnetism Will be induced into thearticles being treated whether a simple direct current is utilized orWhether a current characterized by periodic reversals is employed. Thepolarity of magnetisminduced in a bumper or a rack of bumpers beingtreated is determined by the direction of the current after the lastreversal in the electrolytic treatment step.

While it is less likely that small steel particles will exist Theintensity of the magnetic field produced by the magnetized bumpers maybe suftric current at the end of the electrocleaning treatment, and bysimuitmeously diminishing the magnitude of the current from its maximumprocessing value to substantially zero over the last ten to twentysecond interval of the periodic reversals. The periodic reversal cyclefor this purpose may be made up of equal or unequal portions of anodicand cathodic current flow as will become apparent by reference to theexamples hereinafter appearing. The preferred cycle has proportions ofthree second anodic and three second cathodic. As will become apparentfrom the subsequent examples, a cycle having the proportions of twelveseconds anodic and three seconds cathodic is also effective todemagnetize the article when the current reversals are madeconcomitantly with the diminution of the current over the last l20seconds of the operation. When a simple non-reversing direct current isbeing used during the electrolytic treatment, it is sufficient to beginthe mriodic reversals of current flow simultaneously with the diminutionof the current.

As a consequence, the magnetism induced into the bumpers and otherarticles of magnetizable materials as a result of the electrolytictreatments and the prior manufacturing operations is substantiallyremoved and the steel particles clinging thereto become detached fordispersement into the treatment bath.

Following the various electrolytic pickling and cleaning treatments, thebumpers are then prepared for the final operation of plating with ametal, such as nickel. Ordinarily electroplating utilizes low voltagedirect current and moderate current densities, but for very rapidplating the current density may be further increased. When high currentdensities are used, more rapid deposition occurs but inferior depositsmay result in that metal deposited at very high current density usuallybecomes pulverulent, rough and burnt after a short interval. It has beenfound that high current densities can be used for a limited period oftime as disclosed in the above-identified Grainger patent, and it isadvantageous to follow such operations by a reverse in the direction offlow of the plating current in such a manner as to remove a portion ofthe plated coating, that is, that portion which tends to be burnt orunsatisactory. By alternate plating and deplating operations, that is,by a series of operations alternately applying and removing metal, highamperage can be successfully employed and satisfactory results obtained.The time interval of such operations for removing the undesirable metalis predetermined to obtain desired results.

During the electroplating operation it has been found that numeroussmall particles from the anode become suspended in the electroplatingbath. If these particles are magnetic material, as is the case withnickel, they are magnetically attracted to the steel bumpers which againbecome magnetized whether a simple direct plating current is used orwhether a current characterized by periodic reversals is employed. Assoon as the particles adhere to the cathode surface, such as a bumper,they too become cathodic and the metal being plated deposits on andaround the particle so that it ultimately becomes secured to and a partof the plated coating and causes roughness. Any solid particlessuspended in the bath during plating, whether of magnetic material ornot, may also settle upon the object being plated, particularly theupper horizontal or socalled shelf surfaces, and become secured to theplated coating in much the same manner and cause roughness. Theconventional means of eliminating roughness under these conditions is byusing anode bags or diaphragms to prevent anode particles from reachingthe cathode, and by providing a sufliciently high rate of solutioncirculation through a filter to keep the solution substantially freefrom suspended particles. Shop dirt or air-carried solids in the platingroom also are a source of suspended solids in the plating solutions androughness resulting from these sources is controlled by goodhousekeeping and somet mes air conditioning the plating area.

Because particles in the plating bath causing roughness duringelectroposition of a metal become more or less so cured to the surfaceof the cathode, demagnetizing article: of magnetizable metal during thefinal states of the electro plating operation will not necessarilycompletely eliminate roughness. However, articles of magnetizable metalssuch as steel bumpers, may be effectively demagnetizec' by this meansand from that point any attraction of particles and roughness resultingtherefrom is substantially completely avoided.

This is accomplished in accord with the present invention by reversingthe electroplating current at a fast cycle of approximately /6 cycle persecond (i.e., 3 seconds anodic and 3 seconds cathodic) during the lastthirty seconds of the plating operation and simultaneously steadilydiminishing the current over this last thirty second interval from fullvalue to substantially zero.

It will be appreciated that by demagnetizing the bumpers, a magnet typeof thickness tester can be used to accurately measure the thickness ofthe deposited coating. thus providing for a convenient, non-destructiveand much favored production control.

in order to demonstratevthe demagnetizing effect oi periodicallyreversing the electric current simultaneously with diminishing thecurrent at the end of the electrolytic and the electroplatingoperations, the following examples provide a comparative analysis ofpassing various forms of current through an article of magnetizablematerial. For each of the examples, specially formed miniatureautomobile bumpers were utilized in which the bumper size was scaleddown for the purpose of .convenience to approximately of the actualproduction size. Eight bumpers of scaled-down size were used in eachexample and were mounted back in a rack in two vertical rows of foureach. The rack of bumpers, simulating in every re spect racking inproduction, was immersed in a suitable alkaline electrolytic treatmentbath and the current passed through the bumpers was limited forconvenience to of the normal magnitude generally used during production.

As a consequence the magnetic fields produced were only approximately /3of that intensity normally experienced during production. The directionand intensity of the induced magnetism was measured by means of asensitive compass by placing each of the bumpers along the east-westline passing through the north (i.e., south) pole of the compass needle.The magnetism was measured at each end of each bumper in the rack at twodifferent vertical distances above the ends of the bumpers which arehereinafter referred to as the near and far positions. The square'of theratio of the two vertical distances corresponding to the near and farpositions was maintained for each bumper end at 13 and the deflection ofthe compass needle was observed in degrees. If the north pointingcompass needle was attracted, the end of the bumper was called north andif the compass needle was repellent, the end of the bumper was calledsouth. These compass measurements were made before and afterelectrolysis in an alkaline electrolyte. The bumpers were to allpractical purposes demagnetized before electrolytic treatments, at leastto the extent that any deflection on the compass needles was less than10 degress in the near composition and Zero in the far composition.

EXAMPLE 1 Mild steel model bumpers arranged as described on the modelrack were electrolyzed anodically for 3 minutes in an alkaline solutionat amperes total current without reversing the current. Compassdeflections measured at both the near and the far positions for each endof the bumper were taken before the current was passed through thebumpers and after the current was passed through the bumpers. Thesecompass deflections before and after application of current aretabulated in degrees in Table 1 in the horizontal columns identified asbe- 7 r fore and after. The ends of each bumper are identified in Table1 as end A and end B.

In order to characterize the results of the experiment, the algebraicdifference of the compass deflections before and after application ofcurrent is tabulated in Table 1 in' degrees for each position of thecompass. For example, at the near position, end A of bumper No. 1 wasobserved to have a compassdeflection of 8 degrees north beforeapplication of current and a compass deflection of 33 degrees southafter application of'current in accordance with the current flowprovided in Example 1. The algebraic difierence, which is tabulated inthe horizontal column identified as difierence, is indicated to be 41degrees,

In the last horizontal column in Table l, the summation of thesedifferences. are tabulated separately for the near and far? compasspositions and are referred to as the characteristics of the experiment.Thus, in the near position, the sum of the dilferences in compassdeflections for each of the ends of the numbers are:

degrees. Simila ly, the sum of the differences of the compassdeflections in the far position is tabulated as 31 degrees forExample 1. Thus, the magnitudes of 341 degrees and 31 degreescharacterize the increase in the degree of 'magnetism induced into therackof model bumpers when a total current of 100 amperes is. passedthrough the bumpers for a period of 3 minutes.

Table 1 Compass Deflections Bumper No. Near Position Far Position End AEnd B End A End B 1 (Top bumper on N8 S3 0 rack). S33 N 40 S N7 41 43 57 2 N 3 0 0 0 S12 N23v 0 N2 15 23 O 2 3 N8 0 0 0 55 N 0 0 13 10 0 0 4(Bottom bumper)- S2 N8 0 0 i S2 N8 0 0 a Difference." 0 0 0 0 5 (Topbumper) Before S2 N10 0 0 After N45 S60 N7 1 86' 47 70 7 6 'N 2 S1 0 0N35 S17 N3 81 Difiereuce... 33 16 3 1 7 Before S4 N7 0 0 After N4 S5 0 0Difference." 7 l2 0 0 8 (Bottom bumper). Before S3 N8 0 0 After a. 0 0 00 Difference..- 3 -8 O 0 Characteristic (Sum of all differences). 341 31EXAMPLE 2 A rack of model bumpers was electrolyzed according to Example1, except that the direction of the current was reversed every 3seconds. The characteristics (i.e., the sum of all the differences ofcompass deflections before and after application of current) of this runwas 389 degrees in the near position and 60 degrees in the far position.

EXAMPLE '3 run were 12 degrees and 0 degree in the ?near and farpositions, respectively.

8 EXAMPLE 4 The experiment of Example 3 was repeated, except that thetime during which the current was diminishedwas reduced to 12 seconds.The characteristics of this run were 14 degrees and 0 degree, in thenear and far positions, respectively.

EXAMPLE 5' A rack of model bumpers was electrolyzed according to Example2, except that the periodic. reversal cycle of the current was changedto 12 seconds anodic and 3 seconds cathodic. The characteristics 'ofthis run were .379 degrees and 37 degrees, in the near and far positionsrespectively.

' EXAMPLE 6 will induce substantial magnetism in the articlebeingelectrolyzed. From Example 2, it will be appreciated that merelyreversing the direction of the current every 3 fseconds, Withoutcausingthe current to decay to zero value in the final period of the operation,will not cause the article to become demagnetized and will not prevent'magnetism from being induced into the article.

From Example 3, it is apparent that when'the electrolyzing current isgradually diminished to zero over the last thirty seconds simultaneouslywith the periodic reversal of the current flow in accordance with thepresent invention, the degree of magnetism remaining in the articles issubstantially negligible, particularly in comparison with the magnetisminduced and remaining under the conditions given in Examples 1 and 2.

Examples 4 and 6 indicate that the period over which the currentis'diminished may vary from 12 seconds to 30 seconds for the purpose ofdemagnetizing the article.

It has been found that diminution of the current over the last lO-20seconds ofanelectrolytic alkali or acid treatment is satisfactory todemagnetize the article when the flow of current is simultaneouslyreversed. The preferred period'of current diminution following anelectroplating step, however, is 30 seconds in order to demagnetize thearticle.

Example 5 exemplifies the fact that the degree of magnetism induced intothe article is not diminished by only applying a periodic reversal cyclemade up of unequal portions of anodic and cathodic current.

. From Example 6 it is apparent that the current may be reversed atother than a rate of cycle per second (i.e., 3 seconds anodic and 3seconds cathodic) in order to' demagnetize the article and to produce aproduct from each electrolytic treatment step that is free ofappreciable magnetism induced during that or prior operations.

I Alternating current of the common 60 cycle frequency has been foundnot to induce magnetismwhen thearticle is subjected to conditionssimilar to those associated with using a direct or periodicallyreversingcurrent. On the other hand, such an alternating current does notdemagnetize the article so that any magnetism induced by priortreatments or manufacturing operations will remain.

Since the ditference between periodically reversing the flow of a directcurrent as compared with 60 cycle alternating current is primarily amatter of frequency, there is, consequently, some periodic reversalcycle which, like 60 cycle is not eifective for demagnetizing thearticle.

As a practical matter, however, cycles'faster than 3 secondscathodic and3 seconds anodic (i.e., cycle per second) are not readily obtainablesince the only practical method for reversing the large currentsemployed in electrolytic treatments is to reverse the exciting fieldcurrent of a D.-C. generator. The time required to overcome thehysteresis effect in the generator field coil and to thereby accomplisha current reversal is dependent upon the characteristics of thegenerator and varies on the order of two to four seconds. As aconsequence, the fastest current reversal obtainable with a conventionalD.-C. generator is about 3 seconds minus and 3 seconds plus or cycle persecond.

The electrolytic treatment of articles of magnetizable metal accordingto the present invention and the plated articles produced thereby areparticularly applicable to automobile bumpers, hardware, householdappliances and the like which are subject to induction of magnetism as aresult of the electrolytic treatment or prior manufacturing operations.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiment is therefore to be considered in all respects as illustrativeand not restrictive, the scope of the invention being indicated by theappended claims rather than by the foregoing description, and allchanges which come Within the meaning and range of equivalency of theclaims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States LettersPatent is:

1. In a process of plating a magnetizable article with an electroplatingcycle including at least one treatment in which magnetism is inducedinto the article by the flow of electrical current therethrough andwherein the magnetism induced in said article is destroyed to preventthe adherance of magnetically attractable particles to the article andimprove the quality of the plating produced thereon, the steps of:

(a) immersing said article in an electrolyte;

(b) passing a direct current through the immersed article to efiect saidtreatment;

(c) then passing an electrical current through the immersed article atthe end of the treatment, periodically reversing the direction of flowof the current, and gradually reducing the magnitude of the current fromfull value to substantially zero to thereby demagnetize said article.

2. The process as defined in claim 1, wherein the electroplating cycleincludes at least one magnetism inducing electrolytic treatment prior toplating and the periodically reversed, gradually diminisheddemagnetizing current is passed through the immersed article at the endof the electrolytic treatment.

3. The process as defined in claim 1, wherein the electroplating cycleincludes at least one electrodeposition treatment and the periodicallyreversed, gradually diminished demagnetizing current is passed throughthe immersed article during the terminal portion of theelectrodeposition treatment.

4. The process as defined in claim 1, wherein the direction of flow ofthe demagnetizing current is reversed approximately every three seconds.

5. The process as defined in claim 1, wherein the electroplating cycleincludes at least one electrolytic treatment prior to plating and atleast one electrodeposition type plating treatment and a periodicallyreversed, gradually diminished demagnetizing current is passed throughthe immersed article at the end of each of said treatments.

6. The process defined in claim 1 wherein the current is periodicallyreversed and the magnitude of said current is diminished over the last10 to 30 seconds of the treatment.

References Cited in the file of this patent UNITED STATES PATENTS2,118,174 Doane May 24, 1938 2,451,341 Jernstedt Oct. 12, 1948 2,494,121Grainger Jan. 20, 1950 2,807,363 Hendrickson et a1 Sept. 24, 19572,915,444 Meyer Dec. 1, 1959 2,939,826 Gulick June 7, 1960 OTHERREFERENCES Metal Industry, November 1925, volume 23, No. 11, pages 451,452.

1. IN A PROCESS OF PLATING A MAGNETIZABLE ARTICLE WITH AN ELECTROPLATINGCYCLE INCLUDING AT LEAST ON TREATMENT IN WHICH MAGNETISM IS INDUCED INTOTHE ARTICLE BY THE FLOW OF ELECTRICAL CURRENT THERETHROUGH AND WHEREINTHE MAGNETISM INDUCED IN SAID ARTICLE IS DESTROYED TO PREVENT THEADHERANCE OF MAGNETICALLY ATTRACTABLE PARTICLES TO THE ARTICLE ANDIMPROVE THE QUALITY OF THE PLATING PRODUCED THEREON, THE STEPS OF: (A)IMMERSING SAID ARTICLE IN AN ELECTROLYTE; (B) PASSING A DIRECT CURRENTTHROUGH THE IMMERSED ARTICLE TO EFFECT SAID TREATMENT; (C) THEN PASSINGAN ELECTRICAL CURRENT THROUGH THE IMMERSED ARTICLE AT THE END OF THETREATMENT, PERIODICALLY REVERSING THE DIRECTION OF FLOW OF THE CURRENT,AND GRADUALLY REDUCING THE MAGNITUDE OF THE CURRENT FROM FULL VALUE TOSUBSTANTIALLY ZERO TO THEREBY DEMAGNETIZE SAID ARTICLE.